Using Vista and iTunes 8.2.1.6 the OS will just shut off (no blue screen, no warning of any kind) on my docked TSeries ThinkPad. I mention iTunes because it seems to happen most often when downloading large files (like podcasts). It happens 2-3 times a week and I download podcasts daily so it's not too terrible. But I was hoping someone somewhere has seen this behavior. I have yet to come across anybody complaining about this with recent versions of iTunes.

Thoughts on how to pinpoint the problem would be greatly appreciated also.

Blue screens are really rare these days and are usually associated with problem hardware and their drivers. Have you check to see if updated hardware drivers are available? I'd start with the network driver and the sound driver.

It could be that there is something wrong with one or more of your memory sticks. Try downloading the latest Memtest86+ from here.

You have to burn the files to a cd or copy them to a floppy and boot your computer with it. You need to let the test run for at least one pass and some people even recommend letting it run for 24 hours to guarantee your RAM is stable.